KR102619752B1 - Boron nitride powder, manufacturing method thereof, and heat dissipation member using it - Google Patents

Abstract

The main purpose is to provide boron nitride powder with excellent conductivity and high particle strength. A boron nitride powder having the following characteristics (A) to (C), wherein the primary particles include bulk boron nitride in which flaky hexagonal boron nitride agglomerates to form bulk particles. (A) The particle strength of the bulk particles at a cumulative destruction rate of 63.2% is 5.0 MPa or more. (B) The boron nitride powder has an average particle diameter of 2 ㎛ or more and 20 ㎛ or less. (C) The orientation index determined from X-ray diffraction of boron nitride powder is 20 or less.

Description

Boron nitride powder, manufacturing method thereof, and heat dissipation member using it

The present invention relates to boron nitride (BN) powder, its production method, and its use. In particular, the present invention relates to boron nitride powder, a method for producing the same, and a heat-conducting resin composition using the same.

For heat-generating electronic components such as power devices, transistors, thyristors, and CPUs, how to efficiently dissipate heat generated during use has become an important issue. Conventionally, such heat dissipation measures include (1) making the insulating layer of the printed wiring board on which the heat-generating electronic components are mounted high thermal conductivity, and (2) making the heat-generating electronic components or the printed wiring board on which the heat-generating electronic components are mounted electrically. Mounting to heat sinks via insulating thermal interface materials has been commonly practiced. Silicone resin or epoxy resin filled with ceramic powder is used as the insulating layer and thermal interface material of printed wiring boards.

In recent years, with the high speed and high integration of circuits in heat-generating electronic components and the increase in the density of mounting heat-generating electronic components on printed wiring boards, the heat generation density inside electronic devices is increasing year by year. Therefore, ceramic powders with higher thermal conductivity than before are required.

In addition, with the improvement of the performance of the electronic elements, the insulating layer used also tends to be thinner than the conventional hundreds of ㎛, sometimes becoming more than a few tens of ㎛ and less than 100 ㎛, and the corresponding filler also has an average particle size of several tens to several hundreds of the conventional. Small grain hardening is required from ㎛ to 20 ㎛ or less.

Against the above background, hexagonal boron nitride powder, which has excellent properties as an electrical insulating material, such as high thermal conductivity, high insulation, and low relative dielectric constant, is attracting attention.

However, the hexagonal boron nitride particles have a thermal conductivity of 400 W/(m·K) in the in-plane direction (a-axis direction), but a thermal conductivity of 2 W/(m·K) in the thickness direction (c-axis direction). , the anisotropy of thermal conductivity resulting from the crystal structure and flake phase is large. Additionally, when hexagonal boron nitride powder is filled into a resin, the particles are aligned and oriented in the same direction.

Therefore, for example, when manufacturing a thermal interface material, the in-plane direction (a-axis direction) of the hexagonal boron nitride particles becomes perpendicular to the thickness direction of the thermal interface material, so that the in-plane direction (a-axis direction) of the hexagonal boron nitride particles ) could not sufficiently demonstrate the high thermal conductivity.

In Patent Document 1, it is proposed that the in-plane direction (a-axis direction) of the hexagonal boron nitride particles is oriented in the thickness direction of the high thermal conductivity sheet, and the high thermal conductivity of the hexagonal boron nitride particles in the in-plane direction (a-axis direction) is proposed. It can be performed.

However, in the prior art described in Patent Document 1, (1) the oriented sheets need to be laminated in the next step, which tends to make the manufacturing process complicated, and (2) after lamination and curing, it is necessary to cut them into thin sheets. There was a problem that it was difficult to ensure dimensional accuracy of the thickness of the sheet. In addition, since the shape of the hexagonal boron nitride particles was scale-like, the viscosity increased during filling into the resin and fluidity deteriorated, making high filling difficult.

In order to improve these, boron nitride powders of various shapes that suppress the anisotropy of thermal conductivity of hexagonal boron nitride particles have been proposed.

Patent Document 2 proposes the use of boron nitride powder in which primary hexagonal boron nitride particles are aggregated without being oriented in the same direction, and it is said that anisotropy in thermal conductivity can be suppressed. In addition, as a prior art for producing other agglomerated boron nitride, spherical boron nitride produced by a spray dry method (patent document 3) or boron nitride in aggregate manufactured using boron carbide as a raw material (patent document 4) Agglomerated boron nitride (patent document 5) manufactured by repeated pressing and crushing is also known. However, in reality, these can only produce bulk boron nitride powder with a particle size of more than 20 μm, and it is not possible to obtain bulk boron nitride with a particle size smaller than that.

In addition, for example, SGPS (trade name, manufactured by Denka Co., Ltd.) is commercially available as an agglomerated boron nitride powder with an average particle diameter of 20 μm or less. However, this SGPS has insufficient particle strength and also has a high orientation index, so the heat dissipation property is insufficient.

On the other hand, a method of obtaining spherical boron nitride fine powder using a vapor phase synthesis method has been reported (Patent Document 6), but the particles obtained by this method have a small average particle size and therefore have insufficient heat dissipation properties.

Japanese Patent Publication No. 2000-154265 Japanese Patent Publication No. 9-202663 Japanese Patent Publication No. 2014-40341 Japanese Patent Publication No. 2011-98882 Japanese Patent Publication No. 2007-502770 Japanese Patent Publication No. 2000-327312

In the above-described prior art, the produced agglomerated particles were generally larger than 20 μm, and the problem that agglomerated particles having a particle size smaller than that could not be produced could not be solved. For this reason, in the prior art, it was difficult to produce bulk boron nitride powder of 20 μm or less, which has a small degree of orientation and a high crush strength.

Therefore, the purpose of the present invention is to provide boron nitride powder with an average particle size of 2 μm or more and 20 μm or less, which has excellent thermal conductivity and high particle strength.

As a result of intensive study, the present inventors have found that boron nitride powder with an average particle size of 2 ㎛ or more and 20 ㎛ or less having excellent thermal conductivity and high particle strength can be manufactured by a specific manufacturing method, and completed the present invention. It has arrived.

That is, the embodiment of the present invention can provide the following.

[One]

A boron nitride powder having the following characteristics (A) to (C), wherein the primary particles include bulk boron nitride in which flaky hexagonal boron nitride agglomerates to form bulk particles.

(A) The particle strength of the above-mentioned bulk particles at a cumulative destruction rate of 63.2% is 5.0 MPa or more.

(B) The boron nitride powder has an average particle diameter of 2 ㎛ or more and 20 ㎛ or less.

(C) The orientation index determined from X-ray diffraction of the boron nitride powder is 20 or less.

[2]

A heat dissipation member containing the boron nitride powder described in [1] and having a film thickness of 100 μm or less.

[3]

A method for producing boron nitride powder according to [1],

A pressurized nitriding firing process in which boron carbide having a carbon content of 18% or more and 21% or less and an average particle diameter of 5 μm or more and 15 μm or less is fired in a nitrogen pressurized atmosphere at 1800° C. or more and 0.6 MPa or more;

The fired product obtained by the pressurized nitriding firing process is mixed with a boron source, raised to a temperature at which decarburization can begin, and then heated at a temperature increase rate of 5 ° C./min or less until a holding temperature of 1800 ° C. or higher is reached, and the holding temperature is A decarburization crystallization process to obtain bulk boron nitride by maintaining it in a nitrogen atmosphere,

A production method comprising a pulverizing step of pulverizing the bulk boron nitride obtained by the decarburization crystallization step to obtain boron nitride powder having an average particle diameter of 2 μm or more and 20 μm or less.

[4]

A method for producing boron nitride powder according to [1],

A gas phase reaction process in which boric acid alkoxide gas and ammonia gas are subjected to a gas phase reaction at 750° C. or higher;

The temperature of the intermediate obtained by the gas phase reaction process is raised to a calcination temperature of 1500°C or higher in an ammonia atmosphere of 20% by volume or less up to 1000°C and in an ammonia atmosphere of 50% by volume or more above 1000°C, A crystallization process to obtain bulk boron nitride by performing firing at a firing temperature;

A production method comprising a pulverizing step of pulverizing the bulk boron nitride obtained by the crystallization step to obtain boron nitride powder having an average particle diameter of 2 μm or more and 20 μm or less.

The boron nitride powder obtained by the embodiment of the present invention has an average particle diameter of 2 μm or more and 20 μm or less, and further exhibits the effect of excellent thermal conductivity and high particle strength.

Figure 1 shows a photograph obtained by electron microscope observation of boron nitride powder obtained by the production method of Example 1 of the present invention.
Figure 2 shows a high-resolution photograph (enlarged view) obtained by electron microscope observation of boron nitride powder obtained by the production method of Example 1 of the present invention.
Figure 3 shows a photograph obtained by electron microscope observation of boron nitride powder obtained by the production method in Example 2 of the present invention.
Figure 4 shows a high-resolution photograph (enlarged view) obtained by electron microscope observation of boron nitride powder obtained by the production method of Example 2 of the present invention.

Unless otherwise specified, the numerical range in this specification shall include the upper limit and lower limit. “Part” or “%” in this specification is based on mass, unless otherwise specified. Note that the unit of pressure in this specification is gauge pressure, and notations such as (G) or (gage) are omitted unless otherwise specified.

<1. Boron nitride powder>

The boron nitride powder according to the embodiment of the present invention contains bulk boron nitride in which flaky hexagonal boron nitride primary particles agglomerate to form agglomerates and have the following characteristics.

＜Large boron nitride particles＞

In this specification, “bulky boron nitride particles” or “massive particles” that are not according to the prior art refer to boron nitride particles formed by agglomerating flaky hexagonal boron nitride primary particles into agglomerates. The particle strength (single granule crush strength) of the bulk boron nitride particles determined based on JIS R 1639-5:2007 is 5.0 MPa or more at a cumulative failure rate of 63.2%. If the particle strength is less than 5.0 MPa, the agglomerated particles collapse due to stress during kneading with the resin or during pressing, and a problem occurs in which the thermal conductivity decreases. Additionally, “63.2%” means lnln{1/(1-F(t)) in the Weibull distribution function taught in JIS R 1625:2010 cited by JIS R 1639-5:2007. } = It is known as a value that satisfies 0, and is a value based on the number of particles.

In a preferred embodiment, the particle strength at a cumulative destruction rate of 63.2% of the bulk particles may be 6.0 MPa or more, and more preferably 7.0 MPa or more.

In addition, the upper limit of the particle strength when the cumulative destruction rate of the bulk particles is 63.2% is not particularly limited, but can be manufactured to be, for example, 30 MPa or less, 20 MPa or less, etc.

＜Boron nitride powder＞

The “boron nitride powder” according to the embodiment of the present invention may have an average particle diameter of 2 μm or more, more preferably 4 μm or more, and still more preferably 5 μm or more. Additionally, the average particle diameter of the boron nitride powder may be 20 μm or less, more preferably 19 μm or less, and even more preferably 18 μm or less. The range of the average particle diameter of the boron nitride powder can be 2 μm or more and 20 μm or less, and more preferably 4 μm or more and 18 μm or less.

If this average particle diameter is too small, less than 2 μm, a problem occurs in which thermal conductivity decreases. Additionally, if this average particle diameter is too large, exceeding 20 μm, when producing a sheet with a thickness of several tens of μm, the difference between the thickness of the sheet and the average particle diameter of the boron nitride powder becomes small, making it difficult to manufacture the sheet. There is a risk of sunset.

＜Orientation index of boron nitride powder＞

The orientation index of the boron nitride powder according to the embodiment of the present invention can be determined from X-ray diffraction, and its value is 20 or less, preferably 19 or less, and more preferably 18 or less.

If this orientation index exceeds 20 and is too large, a problem of lowering the thermal conductivity occurs. The lower limit of the orientation index is not particularly limited, but is generally considered to be around 6 even if it is completely random.

In a preferred embodiment, the boron nitride powder may have a thermal conductivity of 6 W/(m·K) or more. By having such a high thermal conductivity together with the high particle strength of the aggregated particles, it can be suitably used as a heat dissipation member for heat-generating electronic components such as power devices, and can be particularly suitably used as a raw material for thin film applications.

＜2. Method for producing boron nitride powder>

The boron nitride powder according to the embodiment of the present invention can be manufactured by any of the following two types of methods.

＜Method (a)＞

Method (a) includes a pressure nitriding sintering process, a decarburization crystallization process, and a grinding process.

＜Pressure nitriding firing process＞

In the pressure nitriding firing process in method (a), boron carbide with a carbon content of 18% or more and 21% or less and an average particle diameter of 5 µm or more and 15 µm or less is used as a raw material. Boron carbonitride can be obtained by subjecting this boron carbide raw material to pressurized nitriding firing in an atmosphere with a specific firing temperature and pressurized conditions described later.

＜Boron carbide raw materials used in the pressurized nitriding process＞

Since the average particle size of the boron carbide raw material affects the average particle size of the finally obtained bulk boron nitride, the average particle size is 5 μm or more and 15 μm or less. It is preferable that the boron carbide raw material does not contain boric acid or free carbon as impurities, except for unavoidable ones, or, if it does contain them, only in small amounts.

The lower limit of the average particle diameter of the boron carbide raw material is preferably 6 μm or more, and more preferably 8 μm or more. If the average particle diameter is smaller than 5 μm, a problem occurs in which the orientation index of the generated bulk particles increases.

The upper limit of the average particle size of boron carbide is preferably 14 μm or less, and more preferably 13 μm or less. If the average particle diameter is larger than 15 μm, the generated bulk particles become too large, and coarse particles are likely to remain even when pulverized, which is not preferable. Additionally, if pulverization is performed until such coarse particles are completely eliminated, the problem of increasing the orientation index also occurs, which is also undesirable.

The carbon content of the boron carbide raw material used in the pressurized nitriding firing process is preferably lower than B ₄ C (21.7%) in the composition, and can preferably be in the range of 18.0% or more and 20.5% or less. The lower limit of the carbon content of the boron carbide is preferably 19% or more. The upper limit of the carbon content of the boron carbide is preferably 20.5% or less. If the carbon content is too high, exceeding 21%, the amount of carbon volatilized during the decarburization crystallization process described later increases too much, making it impossible to produce dense bulk boron nitride, and also causes the problem that the carbon content of the boron nitride ultimately produced becomes too high. Therefore, it is not desirable. Additionally, it is difficult to produce stable boron carbide with a carbon content of less than 18% because the discrepancy from the theoretical composition is too large.

As a method for producing the above boron carbide, a known production method can be applied, and boron carbide with a desired average particle size and carbon content can be obtained.

For example, boron carbide lumps can be obtained by mixing boric acid and acetylene black and then heating the mixture in an inert gas atmosphere at 1800 to 2400°C for 1 to 10 hours. This boron carbide lump can be pulverized, sieved, washed, impurities removed, dried, etc. as appropriate to produce boron carbide powder.

The mixture of boric acid, which is a raw material of boron carbide, and acetylene black is preferably 25 to 40 parts by mass of acetylene black per 100 parts by mass of boric acid.

The atmosphere for producing boron carbide is preferably an inert gas. Examples of the inert gas include argon gas and nitrogen gas, and these can be used individually or in combination as appropriate. Among these, argon gas is preferable.

Additionally, a general pulverizer or pulverizer can be used to pulverize the boron carbide lump, and an appropriate particle size can be obtained by pulverizing the boron carbide lump for, for example, about 0.5 to 3 hours. It is preferable to sieve the boron carbide after pulverization to a particle diameter of 75 ㎛ or less using a sieve.

＜Various conditions in the pressure nitriding firing process＞

The firing temperature in the pressure nitriding firing process is 1800°C or higher, and is preferably 1900°C or higher. Additionally, the upper limit of the firing temperature is preferably 2400°C or lower, and more preferably 2200°C or lower. The range of the firing temperature in a preferred embodiment can be 1800 to 2200°C.

The pressure in the pressure nitriding firing process can be 0.6 MPa or more, and more preferably 0.7 MPa or more. Moreover, the upper limit of the pressure is preferably 1.0 MPa or less, and more preferably 0.9 MPa or less. The range of the pressure in a preferred embodiment may be 0.7 to 1.0 MPa. If the pressure is less than 0.6 MPa, a problem occurs in which nitriding of boron carbide does not proceed sufficiently. Also, from the viewpoint of cost, it is preferable that the pressure is 1.0 MPa or less, but it is also possible to set it to a value higher than this.

As the firing temperature and pressure conditions in the pressure nitriding firing process in a preferred embodiment, the firing temperature can be 1800 to 2200°C and also 0.7 to 1.0 MPa. When the firing temperature is 1800°C, if the pressure is less than 0.7 MPa, nitridation of boron carbide may not proceed sufficiently.

The atmosphere in the pressure nitriding firing process requires a gas in which a nitriding reaction proceeds, and examples include nitrogen gas and ammonia gas, which can be used individually or in combination of two or more. . Among these, nitrogen gas is preferable considering the ease and cost of nitriding. It is preferable that the atmosphere contains at least 95% (V/V) or more of nitrogen gas, and more preferably 99.9% (V/V) or more.

The firing time in the pressure nitriding firing process is not particularly limited as long as nitriding sufficiently progresses, but is preferably 6 to 30 hours, more preferably 8 to 20 hours.

＜Decarburization crystallization process＞

In the decarburization crystallization process in method (a), the boron carbonitride obtained in the pressure nitriding firing process is heated in an atmosphere above normal pressure until the maintenance temperature is reached at a specific temperature increase rate described later, and the boron carbonitride is heated to a constant temperature in a specific temperature range. By performing heat treatment over time, bulk boron nitride particles in which primary particles of flaky hexagonal boron nitride aggregate and form agglomerates can be obtained. That is, in this decarburization and crystallization process, boron carbonitride is decarbonized, formed into flakes of a predetermined size, and these are agglomerated to form massive boron nitride particles.

The temperature at which decarburization can start in the decarburization crystallization process is a temperature that can be set depending on the system. For example, it can be set in the range of 1000 to 1500°C, more preferably in the range of 1000 to 1200°C. Moreover, the atmosphere above normal pressure means that it may be normal pressure (atmospheric pressure) or may be pressurized, but in the case of pressurization, it may be, for example, 0.5 MPa or less, preferably 0.3 MPa or less.

After raising the temperature to the temperature at which decarburization can be started, the rate of increasing the temperature to the holding temperature is 5°C/min (i.e., per minute in degrees Celsius), and is preferably 4°C/min or less, 3°C/min or less, or 2°C/min or less. You can set it below min.

The holding temperature after the above-mentioned temperature increase may be 1800°C or higher, and more preferably 2000°C or higher. The upper limit of the holding temperature is not particularly limited, but is preferably 2200°C or lower, and more preferably 2100°C or lower. If the holding temperature is too low, such as less than 1800°C, there is a risk that grain growth will not sufficiently occur and the thermal conductivity may decrease. On the other hand, if the holding temperature is 1800°C or higher, grain growth is likely to occur favorably and thermal conductivity is likely to improve.

The holding time at the holding temperature is not particularly limited as long as crystallization sufficiently progresses, and in a preferred embodiment, for example, it is in the range of more than 0.5 hours and less than 40 hours, more preferably in the range of 1 to 30 hours. can do. Additionally, the holding time may be preferably 1 hour or longer, more preferably 3 hours or longer, further preferably 5 hours or longer, and even more preferably 10 hours or longer. Moreover, the upper limit of the holding time is preferably 30 hours or less, and more preferably 20 hours or less. When the holding time is 1 hour or more, grain growth is expected to occur satisfactorily, and when the holding time is 30 hours or less, excessive grain growth and a decrease in grain strength can be reduced, and the firing time is long. As a result, it can be expected that industrial disadvantages can be reduced.

In the decarburization crystallization process, decarburization crystallization is performed by mixing a boron source in addition to the boron carbonitride obtained in the pressure nitriding calcination process as a raw material. Examples of the boron source include boric acid, boron oxide, or mixtures thereof (and, if necessary, other additives used in the technical field).

The mixing ratio of the boron carbonitride and boron source can be appropriately set according to the molar ratio. When using boric acid or boron oxide as a boron source, for example, 100 to 300 parts by mass of boric acid and boron oxide can be used, more preferably 150 to 250 parts by mass of boric acid and boron oxide, based on 100 parts by mass of boron carbonitride. .

＜Crushing process＞

Through the pressure nitriding firing process and the decarburization crystallization process, bulk particles in which flaky boron nitride particles (primary particles) are agglomerated can be obtained. Since the bulk particles obtained by this embodiment have high particle strength, they exhibit the effect of maintaining their bulk form and low orientation index even when the average particle diameter after grinding is 2 μm or more and 20 μm or less.

In the grinding process, a general grinder or crusher can be used, and examples include ball mills, vibration mills, and jet mills. In addition, in this specification, “crushing” also includes “disintegration.”

＜Method (b)＞

Method (b) includes a gas phase reaction process, a crystallization process, and a grinding process.

＜Gas phase reaction process＞

In the gas phase reaction process, an intermediate can be obtained by using boric acid alkoxide gas and ammonia gas as raw materials and performing gas phase synthesis at a reaction temperature of 750°C or higher. In the gas phase reaction process, a tubular furnace (the furnace temperature, that is, the gas phase reaction temperature can be 750 to 1,600°C) can be used, an inert gas stream is used as a carrier gas, and boric acid alkoxide is added in the inert gas stream. By volatilizing, a gas phase reaction with ammonia gas can occur.

Examples of the inert gas stream include nitrogen gas, noble gases (neon, argon, etc.).

The reaction time between boric acid alkoxide gas and ammonia gas is preferably set to 30 seconds or less in order to keep the average particle size of the obtained boron nitride powder within a predetermined range.

The boric acid alkoxide is not particularly limited. In a preferred embodiment, as the boric acid alkoxide, it is preferable that the "alkyl group (R)" of "alkoxide (RO-)" is each independently a straight or branched alkyl chain and has 1 to 5 carbon atoms. Specific examples of boric acid alkoxide include trimethyl borate, triethyl borate, and triisopropyl borate. Among these, trimethyl borate is preferable in terms of reactivity with ammonia and availability.

The molar ratio of boric acid alkoxide and ammonia used in the gas phase reaction process is preferably in the range of 1:1 to 10, more preferably 1:1, in order to keep the average particle size of the boron nitride powder within a predetermined range. It can be done as ~ 2.

＜Crystallization process＞

In the crystallization process, the intermediate obtained in the gas phase reaction process is converted into flaky boron nitride. In the temperature conditions of the crystallization process, the temperature is increased from the start of the temperature increase to 1000°C in an ammonia atmosphere containing 20 volume% or less of ammonia gas, more preferably 15 volume% or less. The ammonia atmosphere may include other gases such as inert gases, preferably nitrogen or argon.

Additional temperature increase after reaching 1000°C is carried out until the calcination temperature is reached in an ammonia atmosphere containing 50% by volume or more of ammonia gas from the viewpoint of reducing the amount of oxygen and maximizing the yield. The firing temperature is 1500°C or higher, more preferably 1600°C or higher, and even more preferably 1700°C or higher. The ammonia atmosphere contains an inert gas as another gas, and nitrogen is preferable. The holding time at the firing temperature is preferably 1 to 20 hours.

＜Crushing process＞

Since the flaky boron nitride powder obtained through the above-mentioned gas phase synthesis process and crystallization process has high particle strength, even if secondary particles (agglomerated particles) are pulverized to have the above-mentioned average particle size, it still has a lumpy form and low orientation. It is possible to maintain the index. Therefore, the grinding process can be performed in the same way as method (a).

＜3. Heat conductive resin composition>

According to one embodiment of the present invention, a heat conductive resin composition can also be manufactured by using the boron nitride powder described above. For the production method of this heat conductive resin composition, a known production method can be used. The obtained heat conductive resin composition can be widely used in heat radiation members and the like.

＜Resin＞

Resins used in the heat conductive resin composition include, for example, epoxy resin, silicone resin, silicone rubber, acrylic resin, phenol resin, melamine resin, urea resin, unsaturated polyester, fluorine resin, polyamide (e.g., polyimide) , polyamideimide, polyetherimide, etc.), polyester (e.g., polybutylene terephthalate, polyethylene terephthalate, etc.), polyphenylene ether, polyphenylene sulfide, wholly aromatic polyester, polysulfone, liquid crystal polymer. , polyethersulfone, polycarbonate, maleimide-modified resin, ABS resin, AAS (acrylonitrile-acrylic rubber/styrene) resin, AES (acrylonitrile/ethylene/propylene/diene rubber-styrene) resin, etc. can be used. . In particular, epoxy resin (preferably naphthalene type epoxy resin) is preferable as an insulating layer for a printed wiring board because it is excellent in heat resistance and adhesive strength to copper foil circuits. Additionally, silicone resins are preferable as thermal interface materials because they are excellent in heat resistance, flexibility, and adhesion to heat sinks, etc.

Specific examples of the curing agent when using an epoxy resin include phenol novolac resin, acid anhydride resin, amino resin, and imidazole. Among these, imidazoles are preferable. The compounding amount of this curing agent is preferably 0.5 parts by mass or more and 15 parts by mass or less, and more preferably 1.0 parts by mass or more and 10 parts by mass or less.

The amount of boron nitride powder used in 100 volume% of the heat conductive resin composition is preferably 30 volume% or more and 85 volume% or less, and more preferably 40 volume% or more and 80 volume% or less.

When the amount of boron nitride powder used is 30% by volume or more, thermal conductivity improves and sufficient heat dissipation performance is easily obtained. Moreover, when the content of boron nitride powder is 85 volume% or less, the likelihood of voids occurring during molding can be reduced, and the decrease in insulation and mechanical strength can be reduced.

Various measurement methods are as follows.

(1) Average particle size

The average particle diameter was measured using a laser diffraction scattering method particle size distribution measuring device (LS-13 320) manufactured by Beckman Coulter, without adding a homogenizer to the sample before measurement processing. In addition, the obtained average particle size is the average particle size based on volume statistical values.

(2) Particle strength

Measurements were performed according to JIS R 1639-5:2007. As a measuring device, a micro compression tester (“MCT-W500” manufactured by Shimadzu Corporation) was used. Particle strength (σ: unit MPa) is σ = α × P/(( Measurements were performed on ²⁰ or more particles using the equation π Additionally, when the average particle diameter was less than 2 μm, calculation of particle strength was impossible.

(3) Orientation measurement

An X-ray diffractometer (ULTIMA-IV manufactured by Rigaku Corporation) was used to measure the degree of orientation. A sample was prepared by solidifying boron nitride powder, the sample was irradiated with X-rays, and the peak intensity ratio (002)/(100) of the (002) plane and (100) plane was calculated and evaluated.

(4) Thermal conductivity evaluation method

Thermal conductivity was measured using a sheet made of a heat-conducting resin composition containing boron nitride powder as a measurement sample. Thermal conductivity (H: unit W/(m·K)), thermal diffusivity (A: unit ㎡/sec), density (B: unit ㎏/㎥), and specific heat capacity (C: unit J/(kg·K)) It was calculated as H = A × B × C. The thermal diffusivity was determined by processing a sheet as a sample for measurement into a width of 10 mm x 10 mm x a thickness of 0.05 mm and using a laser flash method. The measuring device used was a xenon flash analyzer (“LFA447NanoFlash” manufactured by NETZSCH). Density was obtained using the Archimedes method. The specific heat capacity was determined using DSC (“ThermoPlus Evo DSC8230” manufactured by Rigaku Corporation). The passing value of thermal conductivity was set at 5 W/(m·K) or more.

(5) Evaluation of unveiling

With respect to the sheet with a thickness of 0.05 mm (film thickness of 50 μm) produced in the thermal conductivity evaluation method (4) above, those that could be visually confirmed to be formed without unevenness were evaluated as ○ (pass), while leveling was performed during production. , those that could not be filmed due to uneven formation were evaluated as × (disqualified).

(6) Carbon amount measurement

The carbon content of boron carbide was measured with a carbon analysis device “IR-412 type” (manufactured by LECO).

Example

Hereinafter, the present invention will be described in detail through examples and comparative examples. Additionally, the present invention is not limited to the following examples.

[Example 1]

In Example 1, boron nitride powder was produced according to method (a). Additionally, the produced boron nitride powder was filled into a resin and evaluated.

(Boron carbide synthesis)

After mixing 100 parts of orthoboric acid (hereinafter abbreviated as "boric acid") manufactured by Nippon Electric Co., Ltd. and 35 parts of acetylene black (product name HS100) manufactured by Denka Co., Ltd. using a Henschel mixer, they were charged into a crucible made of graphite, and heated in an arc furnace with argon. Boron carbide (B ₄ C) was synthesized by heating at 2200° C. for 5 hours in an atmosphere. The synthesized boron carbide mass was pulverized with a ball mill for 1 hour and 40 minutes, sieved using a sieve to a particle size of 75 ㎛ or less, washed with an aqueous nitric acid solution to remove iron and other impurities, filtered and dried, and carbonized with an average particle size of 10 ㎛. Boron powder was produced. The carbon content of the obtained boron carbide powder was 19.9%.

(Pressure nitriding firing process)

Boron carbonitride (B ₄ CN) was obtained by filling the synthesized boron carbide into a crucible made of boron nitride and heating it in a nitrogen gas atmosphere at 2000°C and 9 atm (0.8 MPa) for 10 hours using a resistance heating furnace. ₄ ) was obtained.

(Decarburization crystallization process)

100 parts of synthesized boron carbonitride and 100 parts of boric acid were mixed using a Henschel mixer, then filled into a crucible made of boron nitride, and heated from room temperature under a nitrogen gas atmosphere under a pressure of 0.3 MPa using a resistance heating furnace. The temperature increase rate up to 1000°C was 10°C/min, and the temperature increase rate from 1000°C was 2°C/min, and the temperature was increased to the maintenance temperature of 2000°C. By heating at a holding temperature of 2000°C and a holding time of 5 hours, bulk boron nitride in which primary particles were aggregated and formed into agglomerates was synthesized.

(crushing process)

After the synthesized bulk boron nitride was pulverized using a Henschel mixer, it was classified using a sieve mesh and a nylon sieve with a sieve size of 850 μm. After that, it was pulverized with a jet mill (“PJM-80” manufactured by Daiichi Silyo Co., Ltd.) under pulverizing conditions of 0.3 MPa to obtain boron nitride powder with an average particle diameter of 8 μm.

(charge for resin)

The properties of the obtained boron nitride powder as a filler for resin were evaluated. A mixture of 100 parts of naphthalene type epoxy resin (manufactured by DIC, brand name HP4032) and 10 parts of imidazole (manufactured by Shikoku Chemical Company, brand name 2E4MZ-CN) as a curing agent is mixed to 100% by volume, so that the boron nitride powder is 50% by volume. After mixing and applying it on a PET sheet to a thickness of 0.3 mm, degassing was performed under reduced pressure at 500 Pa for 10 minutes. After that, press heating and pressing was performed for 60 minutes under conditions of a temperature of 150°C and a pressure of 160 kg/cm2 to form a 0.05 mm sheet.

In Table 1 and Table 2 below, the measured values and evaluations are summarized along with other examples and comparative examples. In addition, in the table, examples where application or molding could not be performed due to poor fluidity of the slurry after mixing are indicated with “-” as “filling is not possible.”

[Example 2]

In Example 2, boron nitride powder was synthesized according to method (b) and then filled into a resin.

(Gas phase reaction process)

The core tube was installed in a resistance heating furnace and heated to a temperature of 1000°C. Trimethyl borate (“TMB-R” manufactured by Tama Chemical Co., Ltd.) is introduced into the reactor tube through the introduction tube by nitrogen bubbling, while ammonia gas (purity of 99.9% or higher) is also introduced into the core tube via the introduction tube. did. The introduced trimethyl borate and ammonia reacted in a gas phase in a furnace at a molar ratio of 1:1.2, and were synthesized with a reaction time of 10 seconds to produce white powder. The resulting white powder was recovered.

(crystallization process)

The recovered white powder is filled in a crucible made of boron nitride, set in an induction heating furnace, and then heated in an atmosphere containing 10% by volume ammonia gas up to a temperature of 1000°C in a mixed atmosphere of nitrogen and ammonia, and 50% by volume above 1000°C. In an atmosphere containing % ammonia gas, the temperature was raised to the holding temperature of 1800°C. It was heated at the holding temperature for 5 hours, and after completion of firing, it was cooled and the fired product was recovered.

(crushing process)

After the synthesized bulk boron nitride was pulverized using a Henschel mixer, it was classified through a nylon sieve with a sieve size of 850 μm using a sieve mesh. After that, it was pulverized with a jet mill (PJM-80, manufactured by Daiichi Silyo Co., Ltd.) under pulverizing conditions of 0.3 MPa to obtain boron nitride powder with an average particle diameter of 5 μm.

The resin was filled and evaluated under the same conditions as Example 1.

[Example 3]

In Example 3, agglomerated boron nitride powder was produced under the same conditions as Example 1, except that the grinding time during boron carbide synthesis was changed to 1 hour and 20 minutes and “boron carbide with an average particle diameter of 14 μm” was synthesized.

[Example 4]

In Example 4, boron nitride powder was manufactured under the same conditions as Example 1 except that the jet mill grinding pressure was set to 0.5 MPa.

[Example 5]

In Example 5, the grinding time during boron carbide synthesis was changed to 1 hour and 20 minutes, and “boron carbide with an average particle diameter of 14 μm (carbon content 19.8%)” was synthesized, and the agglomerated boron nitride was milled with a jet mill grinding pressure of 0.5 MPa. Boron nitride powder was prepared under the same conditions as in Example 1 except that it was pulverized.

[Example 6]

In Example 6, boron nitride powder was manufactured under the same conditions as Example 1 except that the temperature increase rate from 1000°C was 0.5°C/min.

[Example 7]

In Example 7, boron nitride powder was manufactured under the same conditions as Example 1 except that the temperature increase rate from 1000°C was 5°C/min.

[Comparative Example 1]

In Comparative Example 1, boron nitride powder was produced under the same conditions as in Example 1, except that the pulverization during boron carbide synthesis was changed to 5 hours, and "boron carbide with an average particle diameter of 2 ㎛" was synthesized to synthesize agglomerated boron nitride. did. Since the average particle size of the obtained boron nitride powder was too small, the particle strength could not be measured.

[Comparative Example 2]

In Comparative Example 2, boron nitride powder was prepared under the same conditions as in Example 1 except that the pulverization time during boron carbide synthesis was changed to 45 minutes and “boron carbide with an average particle diameter of 25 μm (carbon content: 20.1%)” was synthesized. Manufactured.

[Comparative Example 3]

In Comparative Example 3, the pulverization time during boron carbide synthesis was changed to 45 minutes, “boron carbide with an average particle diameter of 25 μm (carbon content 20.0%)” was synthesized, the jet mill pulverization pressure was set to 0.5 MPa, and coarse powder was obtained. Boron nitride powder was prepared under the same conditions as in Example 1, except that it was ground until the powder disappeared.

[Comparative Example 4]

In Comparative Example 4, boron nitride powder was manufactured under the conditions of Example 1 except that the temperature increase rate from 1000°C was 10°C/min.

[Comparative Example 5]

In Comparative Example 5, boron nitride powder was manufactured under the same conditions as Example 2 except that firing was carried out at a temperature of 1000°C in an atmosphere containing 50% by volume ammonia gas. As a result, agglomerated boron nitride with primary particles in the form of flakes was obtained. Instead, boron nitride fine particles with spherical primary particles were obtained. Since the average particle size of the obtained boron nitride powder was too small, the particle strength could not be measured.

The present invention particularly preferably provides a boron nitride powder with excellent thermal conductivity, which is filled in a resin composition for use as an insulating layer of a printed wiring board and a thermal interface material, especially with a film thickness of 100 μm or less, a method for producing the same, and a heat-conducting resin composition using the same. It can be provided and is preferably used as a raw material for heat-radiating members of heat-generating electronic components such as power devices, and the heat-conducting resin composition can be widely used in heat-radiating members and the like.

Claims (4)

A boron nitride powder having the following characteristics (A) to (C), wherein the primary particles include bulk boron nitride in which flaky hexagonal boron nitride agglomerates to form bulk particles.
(A) The particle strength of the above-mentioned bulk particles at a cumulative destruction rate of 63.2% is 5.0 MPa or more.
(B) The boron nitride powder has an average particle diameter of 2 ㎛ or more and 20 ㎛ or less.
(C) The orientation index obtained from X-ray diffraction of the boron nitride powder is 20 or less, and the orientation index is the peak intensity ratio between the (002) plane and the (001) plane of the )] is calculated. A heat dissipation member comprising the boron nitride powder according to claim 1 and having a film thickness of 100 μm or less. A method for producing the boron nitride powder according to claim 1, comprising:
A pressurized nitriding firing process in which boron carbide having a carbon content of 18% by mass or more and 21% by mass or less and an average particle diameter of 5 μm or more and 15 μm or less is fired in a nitrogen pressurized atmosphere at 1800°C or more and 0.6 MPa or more;
The fired product obtained by the pressurized nitriding firing process is mixed with a boron source, raised to a temperature at which decarburization can begin, and then heated at a temperature increase rate of 5 ° C./min or less until a holding temperature of 1800 ° C. or higher is reached, and the holding temperature is A decarburization crystallization process of obtaining bulk boron nitride by maintaining it in a nitrogen atmosphere,
A production method comprising a pulverizing step of pulverizing the bulk boron nitride obtained by the decarburization crystallization step to obtain boron nitride powder having an average particle diameter of 2 μm or more and 20 μm or less. A method for producing the boron nitride powder according to claim 1, comprising:
A gas phase reaction process in which boric acid alkoxide gas and ammonia gas are subjected to a gas phase reaction at 750° C. or higher;
The temperature of the intermediate obtained by the gas phase reaction process is raised to a calcination temperature of 1500°C or higher in an ammonia atmosphere of 20% by volume or less up to 1000°C and in an ammonia atmosphere of 50% by volume or more above 1000°C, and A crystallization process to obtain bulk boron nitride by performing firing at a firing temperature;
A production method comprising a pulverizing step of pulverizing the bulk boron nitride obtained by the crystallization step to obtain boron nitride powder having an average particle diameter of 2 μm or more and 20 μm or less.